ohthetrees
New Member
- Joined
- Jun 28, 2021
- Messages
- 76
I live 8 months a year on a 50' sailboat with 1800w of solar, and a 13.5 kWh bank I made from bare cells. My BMS is an REC Active BMS controlling the whole charge system via a Victron Cerbo GX. It is performing absolutely fantastically when I live aboard.
The problem is my "layup settings" for when I leave the boat for the hurricane season and head back to the USA for 4 months. I want to leave the batteries at roughly 30-50% SOC which is how I understand the batteries are "happiest" for long term storage. The problem is that I need to leave a few systems running (a couple of DC-DC battery chargers for start batteries and bow thruster batteries, and a small fridge for our medications) which are maintained by the solar panels. Normally my BMS "End of Charge" setting is 3.5V/cell which sets SOC to 100% and ends charging. When I left last year I set "End of Charge" to 3.25V/cell which equates to roughly 40% SOC. The loads when I'm not aboard are very low compared to our normal loads, so I thought this setting would be adequate to keep the battery at a partial charge while I was gone. However, when I came back, the battery was disconnected by the BMS because of under voltage, and SOC was 0. The lithium batteries are 100% fine because the BMS did it's job, but we lost contents of the fridge, and the lead acid batteries maintained by the DC-DC chargers.
I think what is going on is that 3.25v/cell just isn't enough for the cells to take a real charge from solar during the day, and even though loads were low, they just weren't recovering during the day from the overnight loads. The 3.25v setting probably would have been adequate with a power supply plugged into the mains, but we are solar only. So my question is, since this BMS doesn't allow my to set a target SOC directly, what settings can I use to keep the batteries at partial SOC while I'm away? Obviously 3.25v is too low, but 3.5v is too high.
Any advice appreciated.
My "normal" REC ABMS settings attached.
The problem is my "layup settings" for when I leave the boat for the hurricane season and head back to the USA for 4 months. I want to leave the batteries at roughly 30-50% SOC which is how I understand the batteries are "happiest" for long term storage. The problem is that I need to leave a few systems running (a couple of DC-DC battery chargers for start batteries and bow thruster batteries, and a small fridge for our medications) which are maintained by the solar panels. Normally my BMS "End of Charge" setting is 3.5V/cell which sets SOC to 100% and ends charging. When I left last year I set "End of Charge" to 3.25V/cell which equates to roughly 40% SOC. The loads when I'm not aboard are very low compared to our normal loads, so I thought this setting would be adequate to keep the battery at a partial charge while I was gone. However, when I came back, the battery was disconnected by the BMS because of under voltage, and SOC was 0. The lithium batteries are 100% fine because the BMS did it's job, but we lost contents of the fridge, and the lead acid batteries maintained by the DC-DC chargers.
I think what is going on is that 3.25v/cell just isn't enough for the cells to take a real charge from solar during the day, and even though loads were low, they just weren't recovering during the day from the overnight loads. The 3.25v setting probably would have been adequate with a power supply plugged into the mains, but we are solar only. So my question is, since this BMS doesn't allow my to set a target SOC directly, what settings can I use to keep the batteries at partial SOC while I'm away? Obviously 3.25v is too low, but 3.5v is too high.
Any advice appreciated.
My "normal" REC ABMS settings attached.